Apparatus for the production of electrolytic tinplate

ABSTRACT

A conductor roll for use in the production of electrolytic tinplate has a cylindrical steel barrel with a coating of aluminum bronze on its outer surface and a coating of copper on the aluminum bronze coating.

United States Patent [56] References Cited UNITED STATES PATENTS3,017,119 H1962 Gibson 117/93.1XPF 2,513,515 7/1950 Powers... 191/1 A2,958,742 11/1960 Palmer 191/1 A FOREIGN PATENTS 555,430 8/1943 GreatBritain 191/1 A Primary Examiner-Arthur L. LaPoint AssistantExaminer-George H. Libman Attorney-Malcolm W. Fraser ABSTRACT: Aconductor roll for use in the production of electrolytic tinplate has acylindrical steel barrel with a coating of aluminum bronze on its outersurface and a coating of copper on the aluminum bronze coating.

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APPARATUS FOR THE PRODUCTION OF ELEKITROLYTIC TINPLATE BACKGROUND OF THEINVENTION The present invention relates to improved apparatus for theproduction of electrolytic tinplate.

It is common practice at the present time to manufacture tinplatecontinuously by passing what is in effect an endless strip of steelthrough various processing zones. The steel strip, which may be anythingup to about 45 inches wide, is passed first through an uncoilin'g. zone,then through a preparation zone in which it is cleaned by both chemicaland mechanical processes, then through an electrolytic plating zone inwhich it is passed through several electrolytic baths, then through thefinishing zone in which it is rinsed and otherwise finished and finallyinto a recoiling or shearing and stacking zone.

The present invention is concerned more particularly with the apparatusused in the plating zone. In this zone the steelstrip passes over afirst roll, known as a conductor roll, whence it passes verticallydownwards through a first electrolytic bath at the bottom of which is afirst turning or sink roll, from which the strip passes verticallyupwards out of the liquid of the bath, over a second conductor roll,vertically downwards into a second bath, around a second turning or sinkroll at the bottom of the second bath, vertically upwards to a thirdconductor roll, and so on through any number of electrolytic baths. Theelectrolyte in each bath may be acidic in nature and hence highlycorrosive and is maintained at a temp erature of up to 200 F. The strippasses through the several baths at a speed which may be as high as1,500 feet per minute or more and as it snakes its way up and downthrough the several baths and around the conductor and sink rolls, eachlimb of each loop must be kept in an accurately vertical constant path,since it passes between vertical anodes arranged one on each side ofeach limb of each loop.

In order that the distance between the strip and the anodes on eitherside of it can be maintained and the anodes on either side of it can bemaintained constant, the strip is maintained under tension throughoutits whole passage through the baths.

The steel strip itself serves as a conductor while it is in the bath andcurrent flows through the strip and conductor roll. For thepassage ofcurrent to be satisfactory, the contact between the strip and theconductor roll must be uniform and tight. Thus there must be no specksof dirt between the strip and conductor roll, nor must there be pits ineither surface, since, if there were, arcing would occur at these pointsof irregularity and the arcing would give rise to imperfect plating.

It will be seen therefore that each conductor roll has to satisfy thefollowing stringent conditions:

1. It must be resistant to the corrosive action of the acid bath, sincethe strip carries the acid up on to the upper conductor rolls.

2. The rolls have to carry a heavy current.

3. The rolls must be accurately cylindrical and highly polished in orderto maintain a perfect contact with the strip.

4. Each roll has to support the tension in two limbs.

5. lt must generally operate at an elevated temperature.

These are not by any means all the conditions which must be satisfied byeach conductor roll,- but they are sufficient to show that these rollsperform an important function in the process. Because of the manyconditions, the rolls are expensive to manufacture.

Such conductor rolls may also be used at other sections of theline, forexample in the cleaning and pickling section, the, chemical treatmentsection and in the reflow section.

Hitherto, each roll has consisted of a steel shaft carrying acylindrical steel barrel which in turn bears a shrunk-on jacket ofwrought copper. The barrel is hollow so that it may be water cooled andis made of steel to support the tensions in the strip, Copper is usedfor the jacket, about 5% to l 1% inches thick, so that the current maybe carried satisfactorily and because copper can easily be machined andwill take a high finish.

It is, however, extremely difficult to coat the steel barrel with a 6inch layer of copper, mainly because of the large size of the barrel,which may be about l8 inches to 24 inches in diameter and about 4 feetin axial length.

The barrel is supported on the shaft with the aid ofa pair of annularspacers located at the ends of the barrel and lying between the barreland shaft. The ends of the shaft protrude from the barrel, through thespacers, serve as bearings for the roll, and serve as currentcollectors.

The. whole of the barrel and protruding ends of the steel shaft need tobe coated with copper. Hitherto, this has been doneby forming forgedand/or rolled copper end jackets and a cylindrical barrel jacket, all ofwhich are secured over their respective portions of the roll. Both theend forged jacket portions and the cylindrical barrel portion of thejacket are difficult to obtain. They are expensive to purchase and canbe obtained only after a waiting period of months. When they have beenobtained, the process of fitting them on to the steel roll and thenwelding them together is also expensive and time consuming. When thishas been done, the barrel portion of the welded jacket is ground toaccurate dimensions and then coated with a thin layer of chromium whichis finally polished to give the necessary good contact surface. Whensuch jacketed rolls need repair, the cost may be as much, or more, thanthat of making a new roll.

Nevertheless, such conductor rolls operate fairly satisfactorily; theirmain disadvantage being that they are expensive and take a long time tomake.

It is an object of the present invention to provide an equivalent rollwhich can be made more cheaply and more easily.

SUMMARY OF THE INVENTION According to the present invention, there isprovided a conductor roll comprising a coaxialassembly of shaft,cylindrical barrel and pair of annular spacers, the spacers beinglocated at the ends of the barrel so as to hold the latter spaced over acentral-body portion of the shaft with the ends of the shaft protrudingfrom the barrel, characterized in that at least the barrel part of theassembly is coated externally with an arcsprayed main coating consistingof copper, stainless steel or monel metal.

According to a further feature of the invention there is provided aconductor roll comprising a coaxial assembly of shaft, cylindricalbarrel and pair of annular spacers, the spacers being located at theends of the barrel so as to hold the latter spaced over a central bodyportion of the shaft with the ends of the shaft protruding from thebarrel, characterized by the combination of features that the barrelpart of the assembly is coated externally with an arc-sprayed maincoating of copper and the ends of the shaft protruding from the barrelare each fitted with a wrought copper sleeve.

According to yet another feature of the invention there is provided amethod of making an electrically conductive roll which is in the form ofa coaxial assembly of shaft, cylindrical barrel and pair of annularspacers, the spacers being located at the ends of the barrel so as tohold the latter spaced over a central body portion of the shaft with theends of the shaft protruding from the barrel, characterized by the stepsof assembling the parts of the roll and then arc-spraying onto at leastthe barrel part of the assembled roll a main coating consisting ofcopper, stainless steel or monel metal.

DRAWINGS FIG. 4 is a sectional view of a fragment of the steel barrelhaving successive coatings of aluminum bronze, and copper.

PREFERRED EMBODIMENTS The roll illustrated in FIG. 1 consists of acoaxial assembly of steel shaft, barrel and pair of annular spacers. Thesteel shaft is shown at A and has a cylindrical central body portion 1dand ends 21 and 12 of reduced diameter. It is made hollow so thatcooling water may be passed through it.

The body portion 10 carries intermediate stiffening annular steel plates13 and i4 and thicker steel annular spacers 15 and 16. One or bothspacers l5 and 16 may be keyed to the shaft as at 8. The center bodyportion 10 of the shaft carries,-with the aid of the spacers, thecylindrical steel barrel l9, and the ends 11, E2 of the shaft and thebarrel 19 are all coated with a layer of copper which, over the barrel,is about one-half inch thick.

in carrying out the present invention, instead of making this copperjacket in three or more parts and welding them together, as has beendone hitherto, the jacket is arc-sprayed on to the steel, so as toproduce a unitaryjacket withoutjoints. The barrel portion 20 ofthejacketis about one-half inch thick and the end portions 21 and 22 are somewhatthicker.

Preferably the part or parts of the assembly to be coated are firstgiven a precoating of a metal, giving high adherence to the steel. Wherethe main coating is copper, the precoating may be aluminum bronze whichis sprayed on, after which the main coating of copper is sprayed on tothe preeoating. The required thickness of coating is built upcontinuously and when the required thickness of copper has beenproduced, the copper is ground and the barrel portion 20 (and it may beother parts also) plated with stainless steel, monel metal, chromium ornickel, which finally is polished to a high finish. Alternatively thesemetals may be arc-sprayed onto the copper.

in an alternative embodiment of the invention, illustrated in FIG. 2,only the barrel 19A and the external faces of the spacers llSA and MAare arc-sprayed, while the ends 11A and 2A of the shaft are covered withwrought copper sleeves and 3E. The ends of the shaft require to besubsequently threaded, and this embodiment has the advantage that forgedcopper will stand threading better than sprayed copper. Neverthelessthis embodiment may have the disadvantage of requiring a welded jointbetween the sprayed and forged metal. In order to avoid such joints,'thesleeves may he shrunk onto the ends first and the sprayed metal may thenbe applied to the barrel and spacers and over the edges of the sleeves,to constitute a single, integral jacket.

In a third embodiment illustrated in FIG. 3 the curved surface ofthebarrel 198 only is sprayed and the ends of the shaft and the externalfaces of the spacers 15A and 16A are covered with forged copperjackets33 and 34.

Any known or suitable method may be used for the arcspraying process.

In one method, those parts of the roll to be sprayed were first roughlythreaded so as to provide increased mechanical adhesion of the sprayedparticles and, at the same time, increase the surface area available forbonding. All sharp edges were removed. The surfaces were then gritblasted to remove corrosion and dirt and, at the same time, furtherincrease the surface area.

The roll was then set up in a chuck, so that it might be rotated duringspraying. All the spraying was done from an electric arc, the moltenparticles being blown on to the roll with the aid of compressed air towhich could be added if desired an inert gas designed to inhibitoxidation.

A prcspray, as shown in FlG. 4 consisting of a coating of aluminumbronze was first applied to the surface 19C, since this alloy has a highadhesion to steel and to the subsequently sprayed copper 43. Thespraying conditions were chosen such as to give coarse particles oftheprespray metal.

A main coating of copper was then arc-sprayed on to the aluminum bronze,the conditions being such as to provide a dense, low-shrink deposit ofcopper.

The spraying was achieved by traversing the spray gun longitudinally ofthe roll at an average distance of 6 inches while the roll was rotatedat a speed of about surface feet per minute. Where the side faces of thespacers were sprayed, this was done by hand, holding the gunapproximately at right angles to these surfaces. 7

The sprayed surfaces were then machined and, in the case of the barrel,the finishing operations such as plating and grinding carried out.

Further particulars of suitable methods of arc-spraying arc to be foundin a. Der Maxchinenmarkt" Nos. 93 and 94 for l8th Nov.

i960 and 24th Mar. I961 respectively, and 1 b. in the textbook entitledMetal Spraying and the Flame Deposition of Ceramics and Plastics," byW.E. Ballard, publishers: Chas. Griffin & Co.

What] claim is:

l. A conductor roll comprising a coaxial assembly of a shaft,cylindrical steel barrel, and a pair of annular spacers, the spacersbeing located at the ends ofthe barrel so as to hold the latter spacedover a central body portion of the shaft with the ends ofthe shaftprotruding from the barrel, aluminum bronze coating on.the outer surfaceof said barrel, and a coating of copper on said aluminum bronze coating.

1. A conductor roll comprising a coaxial assembly of a shaft, cylindrical steel barrel, and a pair of annular spacers, the spacers being located at the ends of the barrel so as to hold the latter spaced over a central body portion of the shaft with the ends of the shaft protruding from the barrel, aluminum bronze coating on the outer surface of said barrel, and a coating of copper on said aluminum bronze coating. 